Biogas: the Energy Revolution’s All-Rounder
Biogas is created during the fermentation of biomass. It is a gas containing methane which, as an adaptable, renewable raw material for power, heat and fuel production, makes a major contribution to secure, environmentally-sound energy supply. Biogas can either be stored or injected into the natural gas grid, which makes it particularly versatile.
Biogas, like natural gas, is a gas mixture consisting chiefly of methane. It is produced by microorganisms as they decompose plants, solid manure and slurry. Biogas is also generated in sewage plants and at landfill sites. The most common method of using biogas for energy production is through converting it into heat and electricity in combined heat and power (CHP) plants. The thermal energy can be used for instance to heat buildings, meaning that the energy is used twice over - and thus particularly efficiently. During the biogas manufacturing process, roughly an equivalent amount of carbon dioxide (CO2) is generated as is absorbed by the energy crops during their growth cycle, or as would be released naturally in the rotting of waste. This makes power and heat from biogas plants particularly climate-friendly.
Heat and power from one energy source
Biogas production also has an indirect impact on climate protection. This is because the controlled fermentation of liquid manure and compostable waste prevents the release of harmful gases such as methane, which has a far more potent influence on the greenhouse effect than CO2. A biogas plant with an installed electrical capacity of around 500 kilowatts (kW) generates around four million kilowatt hours (kWh) of electricity and 4.4 million kWh of heat each year from approximately two million cubic metres (m³) of biogas. This replaces the equivalent of 440,000 litres (L) of fuel oil. As a result, a farmer can generate enough power to supply over 1,000 four-person households each year from one power plant, and the same CHP plant will produce sufficient heat to supply 150 households.
In 2010, Europe’s biogas plants generated some 30 billion kWh of power. In many countries, producers of biogas Photo: Schmack Biogas GmbH are able to sell this power at fixed feed-in tariffs. Germany has pioneered this approach with its Renewable Energy Sources Act, introduced in 2000. Here, plant operators receive between twelve euro cents and 25 euro cents per kWh for the power they feed into the grid - irrespective of the installation size and substrate used. Energy crops and agricultural manure or slurry are the substrates primarily used to generate biogas in Germany. By the end of 2010, the country’s stock of biogas plants numbered almost 6,000 and produced around 53 percent of the power generated from biogas in Europe. Other countries, too, are very active in this field. The second largest market for biogas plants is Great Britain, where power is generated predominantly from landfill gas. Italy ranks in third place. A feed-in tariff of 28 euro cents per kWh of power from agricultural raw materials has also helped to trigger a boom here.
Transporting heat: from biogas plant to public district heating network
Whilst the purchase of electricity by utility companies is governed by legislation, biogas producers are required to market the heat they generate under their own steam. Only in a few rare cases are the heating requirements at the farmer’s own site such that heat pro duced by the biogas plant can be fully exploited there throughout the year. Instead, the heat can be fed, for example, into a district heating network. In addition to residential housing, facilities which require heat over the entire year are particularly appealing to plant operators – these could be municipal buildings such as schools or town halls, elderly care homes, swimming pools, greenhouses or fish farms.
Micro gas grids: from biogas plant to combined heat and power plant
If purchasers of heat are located at too great a distance from the biogas plant, transporting this heat is extremely complex and costly. In these cases, the CHP plant can be constructed where the heat is needed. Here, the biogas is simply transported via dedicated pipes to satellite CHP plants in the town, or directly to heat consumers, and then converted into heat and power on site. The waste heat can then be cheaply distributed where it is required.
Biomethane in the natural gas grid
After processing, biogas can also be injected directly into the existing natural gas grid. In this scenario, it exploits the infrastructure available and finds application as a natural gas equivalent (known as biomethane). In Germany alone, around 100 plants currently feed 67,000 standard cubic metres (Sm3) of biomethane into the grid every hour. Sweden and the Netherlands are also seeing a huge boom in natural gas grid feed-in rates.
Biogas as a fuel
Biogas can also be used as a replacement for natural gas in vehicle fuel. This is the primary use of biomethane in Sweden. Here, buses in the public transport networks of over ten towns run on biomethane.
Fuel from one hectare (ha) of maize allows a vehicle to travel around 70,000 kilometres (km) – one and a half times around the world! Germany now also has biogas filling stations for pure biomethane fuel, and ever more natural gas filling stations are mixing biomethane with their natural gas – at ratios of between five and 50 percent.
Energy that can be stored and used at the drop of a hat
Biogas can be stored without difficulty, meaning that it can be used at any time in any location – irrespective of where it is produced. Hybrid power plants, for example, are able to take advantage of these qualities. They combine different renewable energy sources to complement one another, such that the amount of energy required is always at hand. Owing to its aptitude for storage, biogas is particularly valuable here, as it is able to compensate for fluctuations in other renewable sources such as wind and solar energy. This potential will see the use of biogas intensify in Germany’s imminent energy revolution.